The present invention relates to a brushless motor used in a fan of an on-vehicle air conditioner.
FIG. 3 illustrates a prior art outer-rotor type brushless motor used in a fan of an on-vehicle air conditioner. The motor includes a motor holder 1 having a generally bowl-shaped portion at its center, which has a bottom plate 1a, or a mounting plate. A stator 2 is secured to the bottom plate 1a by screws 11. The stator 2 includes a centerpiece 3, a core 4 and a wire 5 wound about the core 4. The centerpiece 3 includes a tube 3a. The tube 3a rotatably supports a rotary shaft 7 of a rotor 6. A yoke 8 of the rotor 6 is secured to the upper portion of the rotary shaft 7, which protrudes from the tube 3a. The yoke 8 surrounds the stator 2.
A sensor magnet 9 is fitted to the lower portion of the rotary shaft 7, which protrudes from the stator 2. As shown in FIG. 4C, the sensor magnet 9 includes a small diameter portion 9a and a large diameter portion 9b. As illustrated in FIG. 4B, a hole 1b is formed substantially in the center of the bottom plate 1a to receive the lower portion of the rotary shaft 7. The diameter of the hole 1b is greater than that of the small diameter portion 9a of the sensor magnet 9 and is smaller than that of the large diameter portion 9b. As shown in FIG. 4A, connectors 10, which are connected to the wire 5, protrude from the bottom of a flange 3b of the centerpiece 3. An arcuate opening 1c is joined to the hole 1b to expose the connectors 10 (see FIG. 4B) from below.
During assembly, the rotor 6 is attached to the stator 2. The stator 2 is then secured to the bottom plate 1a of the motor holder 1 by a screw 11. At this time, the lower portion of the rotary shaft 7 extends through the through hole 1b and the connectors 10 extend through the opening 1c. Thereafter, the sensor magnet 9 is fitted to the lower end of the rotary shaft 7 from the lower side of the motor holder 1. The small diameter portion 9a is inserted into the hole 1b and the large diameter portion 9b is located below the bottom plate 1a. A fastener 12 is fitted to the lower end of the rotary shaft 7, which fixes the sensor magnet 9 to the shaft 7.
A substrate 13 is fastened to the lower side of the motor holder 1 by one or more screws 14. The substrate 13 is located below the large diameter portion 9b of the sensor magnet 9. The substrate 13 has multiple elements forming an exciting circuit. The exciting circuit supplies exciting current to the wire 5 through the connectors 10. The current generates a magnetic field, which, in turn, rotates the rotor 6 and the sensor magnet 9.
The substrate 13 has a Hall element 15. The Hall element 15 is located in the vicinity of the sensor magnet 9. Rotation of the rotor 6 causes changes in the flux through the sensor magnet 9. The flux changes are detected by the Hall element 15. Accordingly, the rotational angle of the rotor 6 is detected. Exciting current is controlled based on the detected rotational angle.
A lower case 16 is fixed to the motor holder 1 and covers the lower side of the substrate 13.
The shapes of the motor holder 1 and the lower case 16 are modified to match different types of vehicles. However, the stator 2, the rotor 6 and the sensor magnet 9 are standard for all vehicles. That is, the same stator 2, rotor 6 and sensor magnet 9 are used in different types of vehicles.
When assembling the brushless motor of FIG. 3, the rotor 6 is coupled to the stator 2. The stator 2 is then fixed to the bottom plate 1a of the motor holder 1. Thereafter, the sensor magnet 9 must be fixed to the lower portion of the rotary shaft 7 from the lower side of the motor holder 1.
The sensor magnet 9, which is a standardized member, cannot be assembled to the motor until it is known which motor holder 1 will be used. That is, the sensor magnet 9 is assembled to the motor after the type of the vehicle is determined and after the motor holder 1 conforming to the selected vehicle type is manufactured. If the type of the motor holder 1 is changed, the assembly line of the motor must be greatly modified, accordingly. The standardized parts must be stored until the selected type of motor holder 1 is manufactured. This complicates the management of inventory. Further, since the motor holder 1 is added to the assemblage in an earlier step in the assembly line, the size of the assembly line must be relatively large at the upstream stages to accommodate the relatively large motor holder 1. As a result, manufacturing costs are higher.